1. Field of the Invention
The present invention relates to an automatic sampler and a needle of the automatic sampler for an analyzer which performs liquid analysis, such as a liquid chromatograph. More particularly, the needle is subject to a surface treatment or coating which reduces contamination of the needle caused by chemical adsorption.
2. Description of the Related Art
FIG. 4 shows an example of a main portion of a flow path arrangement of an automatic sampler for a liquid chromatograph.
In the automatic sampler shown in FIG. 4, a plunger 3 is designed to perform a reciprocating motion by mechanical force. A liquid sample to be analyzed is stored in a large number of vials (small-volume sample bottles) 8 in advance. The vials 8 are arranged on a rack 81. A needle 7 collects samples from the vials 8. The needle 7 is connected to an injector valve 1 through a looped flexible pipe (hereinafter referred to as “loop”) 6. In addition, the needle 7 is retained by a not-shown drive mechanism so that the needle 7 can move freely among the vials 8, a rinse port 9, and an injection port 5 in accordance with input from, for example, programmed instructions. A valve 2 is a six-position rotary valve with six ports “a” to “f” for switching a flow path of liquid sucked and discharged by the plunger 3. The reference numeral 4 represents a rinse bottle.
The injector valve 1 is connected to a liquid chromatograph apparatus 10 through pipes so as to introduce a liquid sample into a flow path of mobile phase liquid in the liquid chromatograph apparatus 10.
An example of an operational sequence of the sample suction and sample injection processes using an auto-injector as shown in FIG. 4 is as follows.    (1) At sample suction, the valve 2 is switched to communicate port b with port 0, and the injector valve 1 is switched to communicate port d with port e and port b with port c, respectively. At the sample suction position, the needle 7 is dipped into a vial 8, and the plunger 3 is driven to suck a predetermined quantity of liquid sample from the vial 8 into the loop 6 through the needle 7. The sucked liquid sample is collected in the loop 6 so as not to reach the valve 2 or the plunger 3.    (2) Next, the needle 7 is pulled out from the vial 8 and moved to the injection port 5 as shown in FIG. 4.    (3) The injector valve 1 is then switched to communicate port a with port b and port e with port f respectively, as shown in FIG. 4, thereby introducing the sample in the loop 6 into the flow path of the mobile phase liquid. Thus, analysis of the liquid chromatograph is started.    (4) After the needle 7 is moved to a vial 8 containing a sample to be analyzed next, operations (1) through (3) are repeated.
In the automatic sampler as described above, a step of rinsing the needle 7 is necessarily included after any sample is sampled. The rinsing step is very important to avoid mixing a preceding sample into another sample to be analyzed (cross contamination).
In the related art, mainly measures against physical contamination have been taken to prevent cross contamination produced through the intermediation of the needle 7. For example, the needle 7 was rinsed, or the surface of the needle 7 was polished and smoothed to help prevent dirt from adhering thereto. However, contamination of the needle 7 is not limited to only physical contamination.
More specifically, stainless steel is commonly used as a material for making the needle 7. Stainless steel is an alloy with an iron base. Therefore, iron is exposed on the surface of stainless steel microscopically, and accordingly, some amount of sample component is adsorbed on the iron portion of the stainless steel due to the chemical properties of iron. For example, a chemically adsorptive phenomenon is easily produced in basic matter because its hydroxyl group is attracted to iron on the surface of stainless steel. The sample component once adsorbed chemically cannot be removed easily, even if it is vigorously rinsed with organic-solvent-based detergent. Such a sample component adsorbed on the surface of the needle 7 and remaining after rinsing is partially mixed into the next sample to be analyzed. Thus, cross contamination is, though slightly in some cases, brought about.
Such cross contamination caused by chemical adsorption has heretofore been substantially overlooked. In recent years, however, with advances in analytic sensitization, it has become necessary to take effective measures against even slight cross contamination.